UNIVERSITY COLLEGE LONDON EXAMINATION FOR INTERNAL STUDENTS MODULE CODE : CHEM0014 ASSESSMENT : CHEM0014C5UC/ CHEM0014A5UD PATTERN MODULE NAME : CHEM0014 – Inorganic Chemistry LEVEL: : Undergraduate DATE : 12-May-2022 TIME : 10:00 Controlled Condition Exam: 4 Hours exam You cannot submit your work after the date and time shown on AssessmentUCL – you must ensure to allow sufficient time to upload and hand in your work This paper is suitable for candidates who attended classes for this module in the following academic year(s): Year 2020/21 and 2021/22 Additional material Periodic table.pdf, Physical constants.pdf and Character tables.pdf Special instructions N/A Exam paper word count N/A TURN OVER CHEM0014 page 2 of 7 Candidates should attempt ALL questions. The numbers in square brackets in the right- hand margin indicate the provisional allocation of marks to the subsections of a question. 1. Answer ALL parts. (a) The Latimer diagram for ruthenium species in acidic solution (pH = 1) is shown below. (i) Calculate the reduction potential for the non-adjacent couple, X. [2] (ii) Construct a Frost diagram for ruthenium in acidic solution. [4] (iii) Identify which ruthenium species are unstable with respect to disproportionation in acidic solution. Justify your answer(s). [2] (iv) Which ruthenium species is the strongest oxidizing agent in acidic solution, and which is the strongest reducing agent [2] (v) Consider the stability field of water. At pH = 1 which ruthenium species can kinetically and/or thermodynamically oxidize water [2] (vi) A Frost diagram for the first-row transition metals (M) in acidic solution (pH = 1) is shown below. What would happen if excess RuO4– (aq) was added to an acidic solution that contained (where applicable) an M2+ ion [3] (This diagram by Stephen Contakes is licensed under a Creative Commons Attribution 4.0 International License) [Question 1 continued overleaf RuO4 RuO4 – RuO2 2+ 1.00 V 1.60 V 1.50 V Ru(OH)2 2+ Ru3+ Ru2+ 0.86 V 0.25 V 0.46 V Ru X CHEM0014 page 3 of 7 Question 1 continued] (b) Account for each of the following: (i) The dissolution of La(NO3)3 in water forms an acidic solution. [2] (ii) In aqueous solution the formation constant (log10 K1) of 18-crown-6 with Li+ is 1.5 but with K+ is 6.0. [2] (iii) The solubilities of LiF and LiI in water at 25 °C are respectively 0.125 g and 167 g per 100 g water. [2] (iv) Li+ has a stronger interaction with OH– than with SR–. [2] (v) For the successive formation constants of aqueous Cd2+ with Br – , K4 is larger than K3 (log10 K1= 1.56, log10 K2= 0.54, log10 K3= 0.06, log10 K4= 0.37). [2] CHEM0014 page 4 of 7 2. Answer ALL Parts. (a) Derive molecular orbital diagrams for both H2O and H2S (C2v), positioning the molecule in the yz plane. Make reference to symmetry, spatial overlaps and energy differences, and display both diagrams on a single figure to allow a direct comparison of orbital energies between molecules. [20] (b) Predict the relative ligand character ( -donor, -donor, -acceptor) of H2S as a ligand in a transition metal complex as compared to H2O (assuming equivalent stable complexes could be formed). Justify your answer by reference to energy levels in your diagram from part (a) and by making explicit reference to the partial calculation outputs from WebMO shown below. [5] Calculated values for H2O Orbital symmetries: Occupied (A1) (A1) (B2) (A1) (B1) Virtual (A1) (B2) Molecular Orbital Coefficients: MO number: 1 2 3 4 5 Symmetry (A1)–O (A1)–O (B2)–O (A1)–O (B1)–O
Energy (Ha) — -20.24708 -1.22175 -0.57802 -0.42996 -0.38346 MO number: 6 7 Symmetry (A1)–V (B2)–V Energy (Ha) — 0.50820 0.65327 Calculated values for H2S Orbital symmetries: Occupied (A1) (A1) (B2) (A1) (B1) (A1) (B2) (A1) (B1) Virtual (A1) (B2) Molecular Orbital Coefficients: MO number: 1 2 3 4 5 Symmetry (A1)–O (A1)–O (B2)–O (A1)–O (B1)–O Energy (Ha) — -90.73392 -8.63804 -6.27117 -6.26799 -6.26522 MO number: 6 7 8 9 10 Symmetry (A1)–O (B2)–O (A1)–O (B1)–O (A1)—-V Energy (Ha) — -0.88779 -0.53190 -0.35956 -0.27276 0.46684 MO number: 11 Symmetry (B2)—V Energy (Ha) — 0.52763 CHEM0014 page 5 of 7 3. Answer ALL parts. (a) Consider the following list of species: PH3, CH3OH, NEt3, Br – , CN – , CH3, CH3SH Classify their ligand character ( -donor, -donor, -acceptor) in the context of ligand field theory, and arrange them in order from weak field to strong field (spectrochemical series). [5] (b) For each of the following pairs of complexes, indicate which has higher ligand field stabilization energy (LFSE) and BRIEFLY explain why. [Fe(CN)6]3– vs [Fe(CN)6]4– [Cr(H2O)6]3+ vs [Fe(H2O)6]3+ [Fe(CN)6]4– vs [Ru(CN)6]4– [6] (c) With the use of d-level diagrams, explain why [NiCl4]2– is paramagnetic whilst [PdCl4]2– and [PtCl4]2– are diamagnetic. [4] (d) Mo(II) and Cu(II) ions form dimeric acetato complexes of composition M2(OAc)4, in which the local environment of each metal ion is square planar (illustrated for Mo below). Using appropriate d-level diagrams, indicate the electronic configuration of Mo(II) and Cu(II) in these complexes. Discuss any metal-metal bonding resulting from the interaction of the d-levels on the metal atoms. Show that your solution is consistent with equilibrium M-M distances of 2.079 for the Mo(II) dimer and 2.616 for the Cu(II) dimer. [10] CHEM0014 page 6 of 7 4. A PXRD pattern of a sample of a polymorph of titanium dioxide is shown below. The pattern was obtained using Mo Kα1 X-ray radiation (λ = 0.7093 ). (a) The peak labelled A can be indexed as a 220 reflection and the peak labelled B can be indexed as 211. Assuming a tetragonal lattice, use these two peaks to estimate the lattice parameters for this polymorph of titanium dioxide. [6] (b) This polymorph of TiO2 crystallizes in a centrosymmetric space group which has the following symmetry operators: x, y, z; x, y, z; y, x, z; y, x, z; x, +y, +z; +x, y, +z; y, +x, +z; +y, x, +z; plus a further 8 symmetry operators related to the above by an inversion centre at the origin. The atomic coordinates for Ti are (0,0,0) and for O are (0.305,0.305,0). (i) List the positions of all of the atoms within the unit cell and hence determine the number of formula units per unit cell. [3] (ii) Determine the density in g cm 3 for this polymorph of TiO2. [2] (iii) Calculate a Ti—O bond length. [1] [Question 4 continued overleaf CHEM0014 page 7 of 7 Question 4 continued] (c) Assuming zero atomic vibrations, derive a simplified expression for the structure factors Fhkl for this material. Comment on the intensities of the 001 and 102 reflections. [7] (d) (i) Determine the Hanawalt index for this material. [4] (ii) Briefly discuss how the purity of the sample might be assessed from the PDF entry for this material in the ICDD database. [2] END OF PAPER